Some books that have helped and influenced my practice are:

An Unentangled Knowing (sometimes titled Pure and Simple) by Upasika Kee Nanayon 

The Path to Peace by Ajahn Chah (this is small book which is probably an excerpt from a larger book of his collected teachings, such as:

Food for the Heart by Ajahn Chah

Being Nobody, Going Nowhere by Ayya Khema

Who is My Self by Ayya Khema

When Awareness Becomes Natural by Sayadaw U Tejaniya

Present Fresh Wakefulness by Chookya Nyima Rinpoche

Carefree Dignity by Tsoknyi Rinpoche